U.S. patent application number 11/547427 was filed with the patent office on 2007-12-13 for grease composition and grease-enclosed bearing.
This patent application is currently assigned to NTN CORPORATION. Invention is credited to Mitsunari Asao, Masaki Egami, Takayuki Kawamura.
Application Number | 20070287646 11/547427 |
Document ID | / |
Family ID | 35125059 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070287646 |
Kind Code |
A1 |
Kawamura; Takayuki ; et
al. |
December 13, 2007 |
Grease Composition and Grease-Enclosed Bearing
Abstract
The present invention provides a grease composition capable of
securely preventing generation of a low-temperature abnormal noise
when it is cold and a grease-enclosed bearing. A grease composition
comprises a base oil and a thickener, wherein the base oil has a
pour point not more than -50.degree. C. and a kinematic viscosity
not less than 15 mm.sup.2/s at 40.degree. C. The base oil is at
least one oil selected from a PAO oil and a perfluoro ether oil.
The thickener is at least one substance selected from a urea
compound and a fluororesin. A mixing consistency of the grease
composition is in the range of 250 to 350. A grease-enclosed
bearing has an inner ring, an outer ring, rolling elements
interposed between the inner ring and the outer ring, and a grease
composition enclosed on a periphery of the rolling elements. The
grease-enclosed bearing is used for an automotive electric
auxiliary machine.
Inventors: |
Kawamura; Takayuki; (Mie,
JP) ; Asao; Mitsunari; (Mie, JP) ; Egami;
Masaki; (Mie, JP) |
Correspondence
Address: |
James V Costigan;HEDMAN & COSTIGAN
1185 Avenue of the Americas
New York
NY
10036-2646
US
|
Assignee: |
NTN CORPORATION
3066, Aza Oyumida, Oaza Higashikata Kuwana-shi, Mie
Kuwana-shi
JP
511-8678
|
Family ID: |
35125059 |
Appl. No.: |
11/547427 |
Filed: |
March 25, 2005 |
PCT Filed: |
March 25, 2005 |
PCT NO: |
PCT/JP05/05478 |
371 Date: |
September 29, 2006 |
Current U.S.
Class: |
508/590 ;
384/462 |
Current CPC
Class: |
C10M 2211/066 20130101;
F16C 33/6607 20130101; C10M 2211/063 20130101; C10M 2207/0406
20130101; C10M 2215/1026 20130101; C10M 169/02 20130101; C10N
2020/02 20130101; F16C 33/6633 20130101; C10N 2040/02 20130101;
C10M 2207/2805 20130101; C10N 2020/011 20200501; C10M 2211/006
20130101; C10M 2205/0285 20130101; C10M 2205/0206 20130101 |
Class at
Publication: |
508/590 ;
384/462 |
International
Class: |
C10M 169/02 20060101
C10M169/02; C10M 105/18 20060101 C10M105/18; C10M 107/02 20060101
C10M107/02; C10M 107/38 20060101 C10M107/38; C10N 20/02 20060101
C10N020/02; C10N 30/06 20060101 C10N030/06; C10N 40/02 20060101
C10N040/02; F16C 33/66 20060101 F16C033/66; C10N 50/10 20060101
C10N050/10; C10N 30/08 20060101 C10N030/08; C10N 30/00 20060101
C10N030/00; C10N 20/00 20060101 C10N020/00; C10M 115/08 20060101
C10M115/08; C10M 119/22 20060101 C10M119/22 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2004 |
JP |
2004-109558 |
Claims
1. A grease composition comprising a base oil and a thickener,
wherein said base oil has a pour point not more than -50.degree. C.
and a kinematic viscosity not less than 15 mm.sup.2/s at 40.degree.
C.; and said thickener comprises at least one substance selected
from among a urea compound and a fluororesin.
2. The grease composition according to claim 1, wherein a mixing
consistency of said grease composition is in the range of 250 to
350.
3. The grease composition according to claim 1, wherein a content
of said thickener is in the range of 5 to 50 parts by weight based
on 100 parts by weight of the total amount of said base oil and
said thickener.
4. The grease composition according to claim 1, wherein said base
oil comprises at least one oil selected from among a synthetic
hydrocarbon oil and a fluorine oil.
5. The grease composition according to claim 4, wherein said
synthetic hydrocarbon oil is a poly-.alpha.-olefin oil.
6. The grease composition according to claim 4, wherein said
fluorine oil is a perfluoro ether oil.
7. A grease-enclosed bearing comprising an inner ring, an outer
ring, rolling elements interposed between said inner ring and said
outer ring, and a grease composition which is enclosed on a
periphery of said rolling elements, wherein said grease composition
is the grease composition according to claim 1.
8. The grease-enclosed bearing, according to claim 7, which is used
for an automotive electric auxiliary machine.
Description
TECHNICAL FIELD
[0001] The present invention relates to a grease composition
enclosed in a bearing incorporated in various industrial machines,
vehicles, and the like and more particularly, to a grease
composition preferable for a bearing used at a high rotational
speed in a wide temperature range from a high temperature to an
ultra-low temperature at which a low-temperature abnormal noise is
generated.
BACKGROUND ART
[0002] A grease composition is enclosed in a bearing incorporated
in various industrial machines and vehicles to impart lubricity to
the bearing. The grease composition is prepared by kneading a base
oil and a thickener. As the base oil, synthetic oils such as a
mineral oil, an ester oil, a silicone oil, an ether oil, a fluorine
oil, and the like are generally used. As the thickener, metal soap
such as lithium soap, urea compounds, fluororesin are generally
used.
[0003] In recent years, a rolling bearing tends to be used at a
high rotational speed. Thus the grease composition is demanded to
have durability at a high temperature. When the metal soap is used
as the thickener, oxidation of the base oil is accelerated at the
high temperature and thus lubricating action deteriorates.
Regarding the base oil, the grease composition containing the
mineral oil as the base oil thereof is oxidized more readily than
the grease composition containing the synthetic oil as the base oil
thereof and thus has a short lubricating life at the high
temperature. Thus in recent years, the grease composition
containing the synthetic oil as the base oil thereof and the urea
compound or the fluororesin as the thickener thereof is mainly used
for the rolling bearing which is used at the high temperature and
speed.
[0004] As various industrial mechanical members become compact and
have high performance, use conditions tend to be strict.
Consequently the grease composition is demanded to have a higher
lubricating performance and a longer lubricating life. In
compliance with the demand for the longer lubricating life, the
addition of an antioxidant and an antiseptic agent to the grease
composition containing a synthetic oil having a high viscosity as
its base oil and an urea compound as its thickener is investigated.
This grease composition is liable to generate the low-temperature
abnormal noise when it is cold.
[0005] When a pulley and the like to be driven by an engine of a
car is operated when it is cold, there is a case in which an
abnormal noise (hoot noise) is generated when it is cold, namely, a
low-temperature abnormal noise is generated. Although the reason of
the generation of the low-temperature abnormal noise has not been
clarified, it is supposed that the low-temperature abnormal noise
is generated owing to a self-excited vibration of a rolling element
caused by nonuniformity of an oily film of grease. That is, when it
is cold, the oily film of the raceway surface is liable to be
nonuniform owing to a rise of the viscosity of the base oil of the
grease. The oily film causes the coefficient of friction between
the rolling element and the raceway surface to make a slight
periodical change. Thereby the rolling element generates the
self-excited vibration. Owing to the self-excited vibration of the
rolling element, the pulley and the like resonate with the bearing.
As a result, the outer ring vibrates (translational motion) axially
to generate a low-temperature abnormal noise.
[0006] As the grease excellent in the durability at the high
temperature and preventing the generation of the low-temperature
abnormal noise, grease containing mixed oil of synthetic
hydrocarbon oil and ester synthetic oil in which not less than
eight ester groups are disposed like the teeth of a comb at one
side of not less than eight carbon atoms constituting chain-shaped
molecules of oil; an urea compound mixed with the base oil as a
thickener; and dithiophosphate added to the base oil thereof as an
extreme-pressure agent is known (see patent document 1).
[0007] A bearing for use in a pulley of a car in which a grease
composition containing a base oil composed of a mixed oil of
poly-.alpha.-olefin (hereinafter abbreviated as PAO) oil and an
ester oil; an alicyclic diurea compound mixed with the base oil as
a thickener; and zinc dithiocarbamate as an additive added to the
base oil is known. In the bearing, a contact angle is formed by
bringing each of a plurality of balls interposed between an inner
ring and an outer ring both constituting the bearing into contact
with the inner ring or with at least the outer ring at two points
(see patent document 2).
[0008] These attempts are aimed at the stability of the oily film
when it is cold to prevent the generation of the low-temperature
abnormal noise and at a long life of the grease composition at the
high temperature. But these attempts are incapable of obtaining a
sufficient effect in preventing the generation of the
low-temperature abnormal noise.
[0009] Patent document 1: Japanese Patent Application Laid-Open No.
9-208982
[0010] Patent document 2: Japanese Patent Application Laid-Open No.
11-270566
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0011] It is an object of the present invention to provide a grease
composition capable of securely preventing the generation of a
low-temperature abnormal noise when it is cold and a
grease-enclosed bearing.
Means for Solving the Problem
[0012] A grease composition of the present invention comprises a
base oil and a thickener, wherein the base oil has a pour point not
more than -50.degree. C. and a kinematic viscosity not less than 15
mm.sup.2/s at 40.degree. C. The thickener comprises at least one
substance selected from among a urea compound and a
fluororesin.
[0013] The mixing consistency of the grease composition is in the
range of 250 to 350. The base oil is at least one oil selected from
among a PAO oil and a perfluoro ether oil.
[0014] In the present invention, the pour point is a value measured
by using the method specified in JIS K2269, and the mixing
consistency is a value of 60-times mixing consistency measured by
using the method specified in JIS K2220.
[0015] A grease-enclosed bearing of the present invention includes
an inner ring, an outer ring, rolling elements interposed between
the inner ring and the outer ring, and a grease composition
enclosed on the periphery of the rolling elements. The
grease-enclosed bearing is used for an automotive electric
auxiliary machine.
Effect of the Invention
[0016] The grease composition of the present invention contains the
base oil and the thickener. The base oil has the pour point not
more than -50.degree. C. and the kinematic viscosity not less than
15 mm.sup.2/s at 40.degree. C. The thickener is at least one
substance selected from among the urea compound and the
fluororesin. Therefore the grease composition to be enclosed in a
bearing displays a preferable lubricity in a wide temperature range
from a low temperature to a high temperature, is capable of
preventing the generation of the low-temperature abnormal noise
immediately after the bearing starts to operate at the low
temperature, and is capable of maintaining a property excellent in
durability at the high temperature for a long time and thus allows
the bearing to have a long life.
[0017] Because the mixing consistency of the grease composition is
in the range of 250 to 350, the grease composition displays a
preferable lubricity in the wide temperature range from the low
temperature to the high temperature and is capable of preventing
the generation of the low-temperature abnormal noise immediately
after the bearing starts to operate at the low temperature.
[0018] Because the base oil is at least one oil selected from among
the PAO oil and the perfluoro ether oil, the grease composition
maintains the lubricating performance at the high temperature and
is securely preventing the generation of the low-temperature
abnormal noise when it is cold.
[0019] The grease-enclosed bearing has the inner ring, the outer
ring, the rolling elements interposed between the inner ring and
the outer ring, and the grease composition enclosed on the
periphery of the rolling elements. Therefore the grease composition
displays a preferable lubricity in the wide temperature range from
the low temperature to the high temperature and is capable of
preventing the generation of the low-temperature abnormal noise
immediately after the bearing starts to operate at the low
temperature. Further the grease composition is capable of
maintaining the property excellent in durability at the high
temperature for a long time and thus allows the bearing to have a
long life.
[0020] Because the grease-enclosed bearing is used for an
automotive electric auxiliary machine, the grease composition
maintains the lubricating performance at the high temperature and
is securely preventing the generation of the low-temperature
abnormal noise in the car when it is cold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a sectional view of a deep groove ball
bearing.
EXPLANATION OF REFERENCE SYMBOLS AND NUMERALS
[0022] 1: deep groove ball bearing [0023] 2: inner ring [0024] 3:
outer ring [0025] 4: rolling element [0026] 5: cage [0027] 6: seal
member [0028] 7: grease composition
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] It has been found that a grease composition containing a
base oil having a pour point not more than -50.degree. C. and a
kinematic viscosity not less than 15 mm.sup.2/s at 40.degree. C.
has a constant durability at a high temperature and an improved
performance of preventing the generation of a low-temperature
abnormal noise. It is considered that owing to the use of the base
oil, the effect of preventing the generation of the low-temperature
abnormal noise is increased by preventing a rise of the viscosity
of the grease composition when it is cold and an oily film of a
raceway surface of a bearing from becoming nonuniform. The present
invention is based on the above-described finding.
[0030] As the base oil which can be used in the present invention,
a mineral oil, a synthetic oil, and a mixture of the mineral oil
and the synthetic oil which are normally used for grease can be
used when they have a pour point not more than -50.degree. C. and a
kinematic viscosity not less than 15 mm.sup.2/s at 40.degree.
C.
[0031] A pour point depressant such as polymethacrylate may be
added to the base oil to set the pour point of the base oil to not
more than -50.degree. C. To prevent deterioration of the
lubricating performance and a decrease of the lubricating life of
the grease composition at a high temperature and speed, the base
oil is required to have a kinematic viscosity not less than 15
mm.sup.2/s at 40.degree. C. and favorably a high viscosity not less
than 30 mm.sup.2/s at 40.degree. C.
[0032] As the mineral oil, it is possible to list a paraffin
mineral oil and a naphthene mineral oil. As the synthetic oil, it
is possible to list a synthetic hydrocarbon oil, an ether oil, an
ester oil, and a fluorine oil.
[0033] As the synthetic hydrocarbon oil, a PAO oil and the like can
be listed. As the ether oil, a dialkyl diphenyl ether oil, an alkyl
triphenyl ether oil, and an alkyl tetraphenyl ether oil can be
listed. As the ester oil, a diester oil, a polyol ester oil, a
complex ester oil of these oils, and an aromatic ester oil can be
listed.
[0034] As the fluorine oil, a perfluoro polyether oil can be
used.
[0035] In consideration of the lubricating performance and
lubricating life of the grease composition at high temperature and
speed, it is preferable that the grease composition contains a
synthetic oil of a synthetic hydrocarbon oil, an alkyl diphenyl
ether oil, an ester oil, and the fluorine oil. It is especially
preferable that the grease composition contains at least one oil
selected from among the PAO oil which is the synthetic hydrocarbon
oil and a perfluoro ether oil which is the fluorine oil.
[0036] As the above-described PAO oil, normally the above-described
PAO oil is an oligomer of .alpha.-olefin or isomerized
.alpha.-olefin or mixtures of polymers. As examples of the
.alpha.-olefin, it is possible to list 1-octene, 1-nonene,
1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene,
1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene,
1-eicosene, 1-docosene, and 1-tetracosene. Normally, mixtures of
these substances are used.
[0037] As the perfluoro polyether oil, it is possible to use a
compound formed by replacing hydrogen atoms of an aliphatic
hydrocarbon polyether with fluorine atoms. Exemplifying the
perfluoro polyether oil, perfluoro polyether having a side chain
shown by the following chemical formulas 1 and 2 and a
straight-chain perfluoro polyether shown by the following chemical
formulas 3 through 5 are used. These oils can be used singly or as
a mixture thereof. Reference symbols m and n denote integers.
[0038] It is possible to exemplify "FOMBRIN Y" (commercial name,
produced by Montedison Inc.) as a commercially available product
shown by the chemical formula 1, "Krytox" (commercial name,
produced by DuPont Inc.) and "BARRIERTA J" oil (commercial name,
produced by Kluber Inc.) as commercially available products shown
by the chemical formula 2, "FOMBRIN Z" (commercial name, produced
by Montedison Inc.) as a commercially available product shown by
the chemical formula 3, "FOMBRIN M" (commercial name, produced by
Montedison Inc.) as a commercially available product shown by the
chemical formula 4, and "DEMNUM" (commercial name, produced by
DAIKIN INDUSTRIES. LTD) as a commercially available product shown
by the chemical formula 5. ##STR1##
CF.sub.3O--(CF.sub.2CF.sub.2O).sub.m--(CF.sub.2O).sub.n--CF.sub.3
m/n<1 [Chemical formula 3]
CF.sub.3O--(CF.sub.2CF.sub.2O).sub.m--(CF.sub.2O).sub.n--CF.sub.3
m/n>1 [Chemical formula 6]
F--(CF.sub.2CF.sub.2CF.sub.2O).sub.n--CF.sub.2CF.sub.3 [Chemical
formula 5]
[0039] The thickener that can be used in the present invention is a
urea compound, fluororesin powder, and a mixture of the urea
compound and the fluororesin powder. It is preferable to use the
urea compound as the thickener for the above-described synthetic
oil and the fluororesin powder as the thickener for the
above-described perfluoro polyether oil.
[0040] As the urea compound, diurea having two urea bonds in its
molecules is preferable and is shown by the following chemical
formula 6. ##STR2## where R.sub.1 and R.sub.3 indicate any one of
an aromatic hydrocarbon group having 6 to 12 carbon atoms, an
aliphatic hydrocarbon group having 6 to 20 carbon atoms, or an
alicyclic hydrocarbon group having 6 to 20 carbon atoms. R.sub.1
and R.sub.3 may be identical to or different from each other.
R.sub.2 indicates an aromatic hydrocarbon group having 6 to 12
carbon atoms.
[0041] As an example of a method of producing the urea compound, a
diisocyanate compound and an amine compound are prepared to react
with each other by using the isocyanate group and the amino group
in an equivalent. Besides the diurea, polyurea or the like can be
used.
[0042] Powder which has an affinity for the perfluoro polyether oil
and is stable at a high temperature can be used for the fluororesin
which can be used to thicken the perfluoro polyether oil.
Exemplifying the fluororesin, perfluororesins such as
polytetrafluoroethylene (PTFE), a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), a
tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are
preferable. The polytetrafluoroethylene is especially preferable
because it is stable at a high temperature.
[0043] It is preferable that the content of the thickener is in the
range of 5 to 50 parts by weight based on 100 parts by weight of
the total amount of said base oil and said thickener. If the
content of the thickener is less than 5 parts by weight, the grease
composition becomes liquid and has a low viscosity and is thus
liable to leak. Thus it is difficult to enclose the grease
composition in a bearing. If the content of the thickener is more
than 50 parts by weight, the grease composition becomes solid and
the consistency thereof becomes less than 100. Therefore the grease
composition cannot be practically used as grease to be enclosed in
the bearing.
[0044] It is preferable that the mixing consistency of the grease
composition which can be used in the present invention is in the
range of 250 to 350. If the mixing consistency of the grease
composition is less than 250, the grease composition has an
inferior lubricating performance at a low temperature. It is not
preferable that the mixing consistency of the grease composition is
more than 350 because the grease composition is liable to leak.
[0045] The grease composition of the present invention contains the
base oil and the thickener as its essential components. The grease
composition may further contain conventional additives for use in
grease such as an extreme-pressure agent, an antioxidant, a rust
resisting agent, a metal-inactivating agent, an oily agent, and the
like. These additives are shown below.
Extreme-Pressure Agent
[0046] By using the extreme-pressure agent, the withstand load and
extreme pressure resistance of the grease composition can be
improved. For example, it is possible to use the following
compounds as necessary: As organometallic compounds, organic
molybdenum compounds such as molybdenum dithiocarbamate and
molybdenum dithiophosphate; organic zinc compounds such as zinc
dithiocarbamate, zinc dithiophosphate, and zinc phenate; organic
antimony compounds such as antimony dithiocarbamate and antimony
dithiophosphate; organic selenium compounds such as selenium
dithiocarbamate; organic bismuth compounds such as bismuth
naphthenate and bismuth dithiocarbamate; organic iron compounds
such as ferric dithiocarbamate and ferric octynoate; organic copper
compounds such as copper dithiocarbamate and copper naphthenate;
organic lead compounds such as lead naphthene and lead
dithiocarbamate; organic tin compounds such as tin maleate and
dibutyltin sulfide; organic sulfonate, phenate, phosphonate of
alkali metal and alkali earth metal; and organometallic compounds
containing gold, silver, titanium, and the like. As sulfur-based
compounds, it is possible to use a sulfide compound such as
dibenzyl disulfide or a polysulfide compound, sulfurized fats and
oils, compounds of ash-free carbamic acid, thiourea compounds, and
thiocarbonates. As a phosphoric acid-based extreme-pressure agent,
it is possible to use phosphate such as trioctyl phosphate and
tricresyl phosphate; and phosphate compounds such as acidic
phosphate, phosphite, and acidic phosphite. In addition, it is
possible to use a halogen-based extreme-pressure agent such as
chlorinated paraffin or solid lubricants such as molybdenum
disulfide, tungsten disulfide, graphite, polytetrafluoroethylene,
antimony sulfide, and boron compounds such as boron nitride. Of
these extreme-pressure agents, compounds of dithiocarbamic acid and
those of dithiophosphoric acid can be preferably used.
Antioxidant
[0047] As the antioxidant, an age resistor, an ozone deterioration
preventive agent, and an antioxidant to be added to rubber,
plastics, lubricant, and the like can be selectively used. For
example, the following compounds can be used: amine compounds such
as phenyl-1-naphtylamine, phenyl-2-naphtylamine,
diphenyl-p-phenylenediamine, dipyridylamine, phenothiazine,
N-methylphenothiazine, N-ethylphenothiazine,
3,7-dioctylphenothiazine, p,p'-dioctyldiphenylamine,
N,N'-diisopropyl-p-phenylenediamine, and
N,N'-di-sec-butyl-p-phenylenediamine.
[0048] Phenol antioxidants can be also used. As the phenol
antioxidants, 2,6-di-t-dibutylphenol,
n-octadecyl-3-(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate,
tetrakis-(methylene-3-(3',5'-di-t-butyl-4-hydroxyphenyl)propionate)methan-
e, 2,2'-methylenebis-(4-methyl-6-t-butylphenol), and
4,4'-butylidenebis-(3-methyl-6-t-butylphenol) are listed.
Rust Resisting Agent
[0049] As the rust resisting agent, the following compounds can be
used: That is, ammonium salts of organic sulfonic acid; organic
sulfonates of alkali metal and alkali earth metal such as magnesium
barium and calcium; organic sulfonates of zinc; organic
carboxylate; phenate, phosphonate, derivatives of alkyl and alkenyl
succinic acid such as alkyl and alkenyl succinates; partial ester
of polyvalent alcohol such as sorbitan monooleate; hydroxy fatty
acids such as oleoyl sarcosine; mercapto fatty acids such as
1-mercapto stearate or metal salts thereof; higher fatty acids such
as stearate; higher alcohols such as isostearyl alcohol; esters of
higher alcohols and higher fatty acids; thiazoles such as
2,5-dimercapto-1,3,4-thiaziazole, 2-mercaptothiaziazole, and the
like; imidazole compounds such as 2-(decyldithio)-benzimidazole,
benzimidazole, and the like; disulfide compounds such as
2,5-bis(dodecyldithio)-benzimidazole, and the like; phosphate such
as tris(nonylphenyl)phosphite; and thiocarboxylate such as dilauryl
thiopropionate and the like. It is also possible to use corrosion
inhibitors such as nitrite, nitrate, chromate, phosphate,
molybdate, and tungstate all having a function of passivating the
surface of metal.
Metal-Inactivating Agent:
[0050] As the metal-inactivating agent, triazole compounds such as
benzotriazole and tolyltriazole can be used.
Oily Agent
[0051] As the oily agents, the following compounds can be used:
fatty acids such as oleic acid, stearic acid, and the like; fatty
alcohols such as oleyl alcohol, and the like; fatty esters such as
polyoxyethylene stearate, polyglyceryl oleate, and the like;
phosphoric acid; andphosphates such as tricresylphosphate, laurate,
polyoxyethylene oleyl ether phosphate, and the like.
[0052] An example of the grease-enclosed bearing of the present
invention is shown in FIG. 1. FIG. 1 is a sectional view of a deep
groove ball bearing.
[0053] In a grease-enclosed bearing 1, an inner ring 2 having an
inner ring rolling surface 2a on its peripheral surface and an
outer ring 3 having an outer ring rolling surface 3a on its inner
peripheral surface are concentrically disposed, and a plurality of
rolling elements 4 is disposed between the inner ring rolling
surface 2a and the outer ring rolling surface 3a. The
grease-enclosed bearing 1 further includes a cage 5 holding the
rolling elements 4 and a seal member 6 fixed to the outer ring 3.
Grease composition 7 is applied to at least the peripheries of
rolling elements 4.
EXAMPLE
Examples 1 through 13
[0054] The base oil and the thickener were mixed with each other at
ratios shown in table 1 to obtain a grease composition of each of
the examples. Reference symbol MDI in tables 1 and 2 denotes
4,4'-diphenylmethane diisocyanate. The generation of a
low-temperature abnormal noise was measured and a life test of the
grease compositions at a high temperature were conducted on the
obtained grease compositions. The test method and the test
condition are shown below.
Comparison Examples 1 through 10
[0055] The base oil and the thickener were mixed with each other at
ratios shown in table 2 to obtain a grease composition of each of
the comparison examples. In a manner similar to that of the
examples, the generation of the low-temperature abnormal noise was
measured and a life test of the grease compositions at the high
temperature were conducted on the obtained grease compositions.
Measurement of Low-Temperature Abnormal Noise
[0056] 0.9 g of the grease composition of each of the examples and
the comparison examples was enclosed in rolling bearings (6203)
respectively. Each rolling bearing was placed in a cryostat having
a temperature of -50.degree. C. for a certain period of time and
taken out therefrom. Thereafter each rolling bearing was mounted on
a bearing rotating apparatus set to a room temperature. When the
temperature of the rolling bearing became -20.degree. C., the
bearing rotating apparatus was rotated at 2700 rpm under a radial
load of 127 N to aurally check whether the low-temperature abnormal
noise was generated. The generation of the low-temperature abnormal
noise was evaluated by the ratio of the number of the rolling
bearings which generated the low-temperature abnormal noise to the
total of the number of the rolling bearings. Table 1 shows the
evaluated results of the examples. Table 2 shows the evaluated
results of the comparison examples.
Life Test of Grease at High Temperature
[0057] 1.8 g of the grease composition of each of the examples and
the comparison examples was enclosed in rolling bearings (6204)
respectively. The bearing rotating apparatus was rotated at 10000
rpm under an axial load of 67 N and a radial load of 67 N. The time
required for seizing to occur was measured. The temperature of the
bearing was evaluated at 200.degree. C. in the case of the fluorine
grease and at 150.degree. C. in the case of other greases. Table 1
shows the evaluated results of the examples. Table 2 shows the
evaluated results of the comparison examples. TABLE-US-00001 TABLE
1 Example 1 2 3 4 5 6 7 8 9 10 11 12 13 Mixing (part by weight)
Base oil Synthetic hydrocarbon oil A 85 73 70 85 77 -- -- -- -- --
-- -- -- Synthetic hydrocarbon oil B -- -- -- -- -- 85 85 -- -- --
-- -- -- Ester oil B -- -- -- -- -- -- -- 85 85 -- -- -- -- Alkyl
diphenyl ether oil -- -- -- -- -- -- -- -- -- 85 85 -- -- Perfluoro
polyether oil A -- -- -- -- -- -- -- -- -- -- -- 75 -- Perfluoro
polyether oil B -- -- -- -- -- -- -- -- -- -- -- -- 75 Thickener
Urea compound Octylamine 7.6 13.7 15.2 -- -- 7.6 -- 7.6 -- 7.6 --
-- -- Cyclohexylamine -- -- -- 6.6 -- -- 6.6 -- 6.6 -- 6.6 -- --
p-toluidine -- -- -- -- 10.7 -- -- -- -- -- -- -- -- MDI 7.4 13.3
14.8 8.4 12.3 7.4 8.4 7.4 8.4 7.4 8.4 -- -- Fluororesin (PTFE) --
-- -- -- -- -- -- -- -- -- -- 25 25 Properties 60-times mixing
consistency 284 240 219 278 318 276 291 251 255 293 286 285 275
(JIS K2220) Low-temperature abnormal 0/10 2/10 3/10 0/10 0/10 0/10
0/10 3/10 2/10 2/10 2/10 0/10 0/10 noise Life at high temperature
3800 3100 2700 4200 3900 4100 3700 3500 3600 2300 2800 5100 6800
(hour) Pour Kinematic point viscosity(40.degree. C.) Maker
Commercial name Synthetic hydrocarbon oil A -57.degree. C. 47
mm.sup.2/s Nippon Steel Chemical Co., Ltd. SHINFIELD 801 Synthetic
hydrocarbon oil B -50.degree. C. 63 mm.sup.2/s Mitsui Chemicals,
Inc. LUCANT HC10 Ester oil B -52.degree. C. 33 mm.sup.2/s Kao
Corporation KAOLUBE 268 Alkyl diphenyl ether oil -50.degree. C.
31.1 mm.sup.2/s Matsumura Oil Presearch Corp. MORESCO HILUBE LB32
Perfluoro polyether oil A -67.degree. C. 65 mm.sup.2/s DuPont L-65
Perfluoro polyether oil B -67.degree. C. 100 mm.sup.2/s DuPont
L-100
[0058] TABLE-US-00002 TABLE 2 Comparison Example 1 2 3 4 5 6 7 8 9
10 Mixing (part by weight) Base oil Synthetic hydrocarbon oil 85 85
-- -- -- -- -- -- -- -- Ester oil A -- -- 85 85 -- -- -- -- -- --
Ester oil B -- -- -- -- -- -- -- -- 89 -- Alkyl diphenyl ether oil
-- -- -- -- 85 85 77 -- -- -- Mineral oil -- -- -- -- -- -- -- 85
-- -- Perfluoro polyether oil -- -- -- -- -- -- -- -- -- 76
Thickener Lithium 12-hidroxystearate -- -- -- -- -- -- -- -- 11 --
Urea compound Octylamine 7.6 -- 7.6 -- 7.6 -- -- 7.6 -- --
Cyclohexylamine -- 6.6 -- 6.6 -- 6.6 -- -- -- -- p-toluidine -- --
-- -- -- -- 10.7 -- -- -- MDI 7.4 8.4 7.4 8.4 7.4 8.4 12.3 7.4 --
-- Fluororesin (PTFE) -- -- -- -- -- -- -- -- -- 24 Properties
60-times mixing consistency 273 271 260 264 287 277 302 257 251 287
(JIS K2220) Low-temperature abnormal 7/10 6/10 6/10 7/10 7/10 8/10
8/10 2/10 0/10 7/10 noise Life at high temperature 3100 3700 1800
1400 4100 4300 4600 370 740 3800 (hour) Pour Kinematic point
viscosity(40.degree. C.) Maker Commercial name Synthetic
hydrocarbon oil -47.5.degree. C. 152 mm.sup.2/s Nippon Steel
Chemical Co., Ltd. LUCANT HC20 Ester oil A -42.degree. C. 27
mm.sup.2/s AKZONOBEL KL305 Ester oil B -52.degree. C. 33 mm.sup.2/s
Kao Corporation KAOLUBE 268 Alkyl diphenyl ether oil -40.degree. C.
97 mm.sup.2/s Matsumura Oil Presearch Corp. MORESCO HILUBE LB100
Mineral oil -50.degree. C. 8.5 mm.sup.2/s NIPPON OIL CORPORATION
KRISEF FB Perfluoro polyether oil -36.degree. C. 160 mm.sup.2/s
DuPont GPL-105
[0059] It is understood from tables 1 and 2 that the bearings in
which the grease compositions of the examples each containing the
base oil having the pour point not more than -50.degree. C. were
enclosed generated much less low-temperature abnormal noise than
the bearings in which the grease compositions of the comparison
examples were enclosed. This is because owing to the use of the
base oil, a rise of the viscosity of the grease composition when it
is cold is prevented, and the oily film of the raceway surface of
the bearing is prevented from becoming nonuniform. Thereby the
effect of preventing the generation of the low-temperature abnormal
noise increased. Therefore the grease composition can be preferably
used for a bearing to be used when it is cold and particularly for
a bearing for use in an electric auxiliary machine.
INDUSTRIAL APPLICABILITY
[0060] The grease composition of the present invention displays a
preferable lubricity in a wide temperature range from a low
temperature to a high temperature and is capable of preventing the
generation of the low-temperature abnormal noise immediately after
a bearing starts to operate at the low temperature. Therefore the
bearing in which the grease composition of the present invention is
enclosed can be preferably used for a vehicle such as a car when it
is cold.
* * * * *